Computer technology is continually advancing, expanding the need for computers in the personal, business, and academic fields. As the need for computers has grown, so too has the need for various peripheral devices for use with computers, such as printers. One type of printer that can be used with computers is referred to as a "thermal" printer. A thermal printer uses a "pen" to apply small droplets of ink to paper to generate a printed version of data (whether it be text pictures, etc.). In a thermal printer, the amount of ink in each droplet is dependent on, among other factors, the temperature of the pen. When the pen is too hot, the droplets are too large, whereas when the pen is too cold, the droplets are too small. Thus, the temperature of the pen in a thermal printer should be regulated carefully in order to achieve an acceptable level of print quality.
The temperature of the pen in a thermal printer can be regulated by supplying energy to the pen in order to heat it, a process referred to as "pulse warming". In order to determine when the pen should be heated, the current temperature of the pen is compared to the temperature the pen should be at for printing (the target temperature). The target temperature is typically hotter than the normal "room" temperature that the printer is located in. If the pen is too cool then pulse warming is used to heat it. If the pen is too hot, then the system waits for the pen to cool down.
In order to accurately compare the current pen temperature to a target temperature, an accurate target temperature must be available to the printer. Various circuitry can be included in a printer to identify a target temperature. However, due to variations in the fabrication process of the circuitry used in the printer, the actual target temperature identified by the circuitry may vary from printer to printer. Such differences in actual versus designed target temperature can affect the print quality of the printer and, if large enough, can actually prevent printing.
One solution to this problem is for each printer to use a channel of a digital to analog converter to generate indication of the target temperature. However, situations can arise where adding a digital to analog converter, or adding an additional channel to a digital to analog converter, is not a desirable option (e.g., there may be design time constraints or hardware cost constraints that make such an addition unattractive). Therefore, it would be beneficial to be able to accurately identify the target temperature without requiring such an additional digital to analog converter or converter channel.
The invention described below addresses these and other disadvantages of the prior art, providing improved pen temperature control in a thermal printer.